The present invention relates to a new and improved method of regulating the level of the molten metal in the molds of continuous casting plants or installations, wherein deviations from a reference value as determined by measuring the level of the molten metal in the mold are overcome by regulating the metal infeed to the mold and/or by regulating the withdrawal speed of the strand from the mold.
It is known during continuous casting of metals to employ a molten metal level regulation or control wherein initially by carrying out an infeed regulation, for instance by means of a stopper, the degree of filling or molten metal level in the mold is regulated in accordance with a prescribed or preset reference value. If the degree of filling of the mold exceeds predetermined or preset boundaries of such reference value, then there is switched over from the metal infeed regulation to a regulation of the withdrawal speed i.e. the casting speed of the strand. During regulation of the withdrawal speed the sets of drive rolls conveying the continuously cast strand are controlled such that by slowing down or accelerating the withdrawal speed of the strand there is maintained the required level of the molten metal in the mold. The withdrawal regulation first then becomes operational when the deviation of the level of the molten metal in the mold from the reference value has exceeded a predetermined upper or lower boundary value.
Such type regulation with switching-over or reversal from the metal infeed regulation circuit to the strand withdrawal regulation circuit and vice versa possesses the drawback that at the moment of switching-over from the regulation of the stopper to the regulation of the withdrawal of the casting or strand, the control or regulator for the withdrawal speed has delivered thereto the maximum deviation signal of the level of the molten bath, because the withdrawal regulation has not followed the actual value of the molten bath level. Hence, related to the reference value, there initially occurs a sudden drop or rise in the level of the molten metal in the mold. During sudden rise of the level of the molten metal there however occurs an immediate switching back to regulation of the stopper, so that initially it is not possible to prevent an unrest or surging of the regulation. This occurs in that each time there is reached the switch-over value from the metal infeed regulation to the strand withdrawal control the regulation again switches back to regulation of the stopper, again resulting in a drop or rise in the molten bath level. Hence, upon reaching the transition conditions from the regulation of the stopper to the regulation of the withdrawal of the strand there arises a frequent switching from the one to the other regulation circuit, producing a so-called surging or hunting of the regulation system. As a result, there prevail unavoidable disturbances, such as overflow of the liquid steel from the upper edge of the mold during operation as well as break-outs in and beneath the mold, requiring increased expenditure in the supervision and maintenance of the continuous casting installation by the operating personnel. However, also at the region of the simultaneous working of the infeed regulation circuit and the withdrawal regulation circuit there hardly can be attained a constant bath level in the mold, since due to the simultaneous action of both circuits each circuit is influenced by the other, generally resulting in an unsuitable regulation. Additionally, the strand withdrawal speed considerably deviates from the desired speed, with the result that the quality as well as the continuous operation, that is the economies of the installation, are considerably impaired.